gitweb: Fix typo in hash key name in %opts in git_header_html

The name of the key has to be the same in call site handle_errors_html
and in called subroutine that uses it, i.e. git_header_html.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 934aacb..e108bbc 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -3220,7 +3220,7 @@
 	}
 	print $cgi->header(-type=>$content_type, -charset => 'utf-8',
 	                   -status=> $status, -expires => $expires)
-		unless ($opts{'-no_http_headers'});
+		unless ($opts{'-no_http_header'});
 	my $mod_perl_version = $ENV{'MOD_PERL'} ? " $ENV{'MOD_PERL'}" : '';
 	print <<EOF;
 <?xml version="1.0" encoding="utf-8"?>